Chromatography is a well-established and valuable technique for separating chemical and biological substances and is widely used in research and industry, finding many applications in compound preparation, purification and analysis. There are many different forms of chromatography, liquid chromatography being of particular importance in the pharmaceutical and biological industries for the preparation, purification and analysis of proteins, peptides and nucleic acids.
A typical liquid chromatography apparatus has an upright housing in which a bed of packing material, which is usually particulate in nature and consists of a porous medium, rests against a permeable retaining layer. A liquid mobile phase enters through an inlet, for example at the top of the column, usually through a porous, perforated filter, mesh or frit, moves through the bed of packing material and is removed via an outlet, typically through a second filter, mesh or frit.
Columns used in liquid chromatography typically comprise a tubular body enclosing the porous chromatography medium through which the carrier liquid or mobile phase flows, with separation of substances or analytes taking place between the mobile phase and solid phase of the porous medium. Typically, the porous medium is enclosed in the column as a packed bed, generally formed by consolidating a suspension of discrete particles, known as slurry that is pumped, poured or sucked into the column, usually from a central bore or nozzle located at one end of the column. The production of a stable, even bed is critical to the final separation process and optimum results are found using bores which are centrally positioned through the column end. Systems for producing such stable, even beds are known in the art and include, for example, compressing the bed by means of an end unit.
Following column packing and prior to use it is necessary to install the column by connecting it to a chromatography system, usually comprising a pump, detectors and inlet and outlet manifolds. When installing the column, it is essential to avoid any draining of the column from liquid as well as to avoid introduction of air into the column and the packed bed, respectively. Furthermore, it may be necessary to purge the system employing the column of any air upstream of the column. Typically, prior art columns and systems accomplish column installation and/or purging or venting by means of a valve (a “vent” or “purge” valve) at one end of the column, usually at its base.
In practice, the valve is used together with the column, which means that the column is connected and disconnected from the system upstream of the valve. For a disposable column, the introduction of such an additional valve is costly. By virtue of its position, it increases both the risk of siphoning of liquid from the column and also the likelihood of further air being introduced into the column. Furthermore, the position of the valve imposes constraints on locating the column within the laboratory and can cause problems in terms of user accessibility, since access to both the top and bottom of the column is required.
JP 63293456 (Sekisui Chemicals Co.) describes a column holder to support columns having been prepared with a stationary phase and being equipped with a discharge aperture at the base and a ventilation device at the top. The column holder is designed such that on the application of gravity or a centrifugal force, to facilitate chromatographic separation of materials on the stationary phase, any surplus fluid remaining above the stationary phase can be removed without allowing air to enter the stationary phase within the column. The discharge aperture is connected to a conduit which is branched at a position that is at the same or a higher level than the upper end of the stationary phase solution and has three open ends, a first at the connection point with the discharge aperture, a second at a position above the surface level of the solution and a third located below the level of the discharge aperture. The conduit is configured such that any surplus fluid can be removed from the column through the third open end where it is collected in an acceptor vessel.
Despite the high level of activity in the field of chromatography over many years there is still a need for a simple axial column that obviates the need for a vent valve or complex column holder and reduces the risk of air entering the column and/or liquid siphoning from it. To date, no axial chromatography columns are available which meet this need and/or provide improved user accessibility.